1. Field of the Invention
The present invention relates to a resilient support mechanism for resiliently supporting the component structure of a wheeled vehicle. More particularly, the present invention is concerned with a control system for a resilient support mechanism such as a suspension mechanism disposed between an unsprung mass and a sprung mass of the wheeled vehicle for controlling a damping force or a damping coefficient of a shock absorber or damper device assembled therein.
2. Discussion of the Prior Art
In a conventional suspension mechanism of a wheeled vehicle, an amount of movement state of a sprung mass or an unsprung mass of the vehicle is detected to determine a target damping force or a target damping coefficient on a basis of the detected amount of movement state thereby to adjust the damping force or damping coefficient of a shock absorber or damper device assembled in the suspension mechanism to the target damping force or damping coefficient. Disclosed in Japanese Patent Laid-open Publication No. 10-119528 is a control system for the suspension mechanism in which the well-known sky nook theory is applied to determine a target damping coefficient based on acceleration of the sprung mass and relative velocity of the sprung mass to the unsprung mass in a vertical direction.
In the suspension mechanism described above, however, the damping force of the shock absorber or damper device is defined by the product of the relative velocity of the sprung mass to the unsprung mass and the damping coefficient, while the damping coefficient changes nonlinearly in accordance with the relative velocity of the sprung mass. For this reason, the design of the control system becomes very complicated. For example, it has been considered to estimate a plant indicative of a state space in the suspension mechanism for design of the control system. However, as the plant is bilinear, it is obliged to apply an approximate law to a range where a control input would not be realized in the resilient support mechanism such as a suspension mechanism, even if a linear control theory was applied to the bilinear system. For this reason, a control specification (a norm condition) given at a design stage may not be theoretically satisfied. As a result, the control input becomes discontinuous to cause a sense of incongruity in control of the suspension mechanism.